In recent years, a computer which can be installed in a vehicle such as a car navigation system using a GPS (Global Positioning System), an in-vehicle PC (hereinafter, referred to as an in-vehicle computer) or the like has become popular as means for routing assistance to a destination. Such an in-vehicle computer provides a driver with routing assistance to a destination by displaying a map based on current location information, and also provides spot information including tourist attractions and gas stations in the areas around the route. Map information and spot information are stored in a storage medium such as a DVD, a HDD or the like. However, since this type of information is frequently subject to changes and thus immediately becomes obsolete, this information needs to be updated along with such changes.
Regarding such updating of information, a car navigation device and a map information providing device are known for being able to obtain updated map information in case that map information is changed. When this car navigation device determines that particular map information is out-of-date, the car navigation device described above can download map information from the map information providing device and update the same.
However, downloading all of map data that become large volumetric produces unnecessary network traffic, and therefore, it takes a long time to acquire the information.